A Bourdon tube pressure gauge comprises, a housing containing a sensing element, i.e., a Bourdon tube in an arc shape. The interior of the Bourdon tube is connected by a hollow coupling to a source of pressure to be measured. A change in the measured pressure causes elastic distortion of the Bourdon tube and a change in the arc shape. The end of the Bourdon tube undergoes displacement, which is translated by a pointer mechanism, to become a corresponding angular displacement of a pointer over a dial. The angular position of the pointer is proportional to the measured pressure that is indicated by a gradient scale on the dial. The hollow coupling extends into the hollow housing in which are mounted, the Bourdon tube, the pointer mechanism and the pointer. The interior of the housing is under atmospheric pressure that counteracts the pressure to be measured. Accordingly, the pointer indicates gauge pressure, i.e. differential pressure between atmospheric pressure on the Bourdon tube and the pressure being measured by the Bourdon tube.
A differential pressure gauge measures differential pressure between two sources of pressure other than atmospheric pressure. The differential pressure gauge has a housing containing a first Bourdon tube that measures a first pressure. The interior of the housing is filled with a fluid. Further, the housing interior has an expansible bladder immersed in the fluid. The interior of the bladder is connected by another hollow coupling to communicate with a source of second pressure. Expansion and contraction of the bladder in response to changes in the second pressure, causes a corresponding change in the pressure of the fluid, which counteracts displacement of the Bourdon tube in response to changes in the measured first pressure. Thus, the pointer indicates a differential pressure between the first measured pressure and the second measured pressure.
Prior to the invention, a conventional engineered fluid delivery process required control of fluid pressure, at an inlet end, to remain within an upper limit, as measured by a Bourdon tube gauge. Further, the engineered process required measurement of differential pressure from an inlet end to an outlet end of a fluid delivery conduit, for example, to determine delivery efficiency, mass flow rate and total mass flow, of the fluid being delivered. Thus, a second gauge was required, either a second Bourdon tube gauge at the outlet end, or a differential Bourdon tube gauge. The two gauges, at the inlet and outlet ends, were located at some distance apart, which caused delay in recording the readings of the gauges. Further, gauge calibration and maintenance were repeatedly performed for two gauges.